When a ship experiences an incident or a peril of the sea and it is carrying liquid cargo such as hydrocarbons, the question arises of being able to evacuate that cargo so as to prevent it from being immobilized or to avoid major pollution, such as that experienced in recent shipwrecks that has been a major topic in the news.
The techniques used to achieve these goals differ depending on whether the ship is submerged or partially out of the water.
In the first case, i.e., in the case of a completely submerged ship, techniques are traditionally used in which seawater is brought into the tanks where the liquid to be recovered is located: under the effect of the hydrostatic pressure, that seawater chases out the liquid in the tank, which is not miscible with the water, thereby making it easy to recover said liquid through flexible discharge pipes.
In the second case, where the ship remains partially out of the water, it is not possible to use the hydrostatic pressure of the water to recover all of the contents of the tanks, and pumping means must be used to extract the rest of the liquid.
To that end, traditionally, either one lowers pumps into the tanks, the pumps being connected to delivery hoses for lifting liquid toward the outside of the tank, or a pump is placed on the deck provided with a hose to suction the contents of the tank toward the outside.
A lift pump refers to a pump which, submerged in the fluid to be displaced, “pushes” it in the delivery pipe; a suction pump refers to a pump that is placed above the fluid to be displaced and “suctions” it through a depressurization phenomenon of the volume comprised between the pump and the fluid.
In the case where pumps are lowered inside the tanks, it is difficult orient them inside the tanks, and it is not uncommon for them to become jammed behind equipment (channels, ladders, stairs, pumps, etc.) or reinforcing elements (beams, ribs, frames, etc.) situated inside the tanks.
Furthermore, the delivery hoses to which they are connected are massive, and make it awkward and lengthy to install those pumps on the operating sites.
In the case of suction from the deck, physical constraints limit the maximum pumping height.